Uniflow cyclones which operate in accordance with the principles described, generally comprises a flow housing or duct provided with swirl-inducing vanes which impart a rotation to the gas stream traversing the duct. This rotation or cyclonic action tends to throw entrained particles outwardly and these particles can be collected in a chamber provided outwardly of the duct mouth.
Such swirl-inducing vanes, which can surround a central body, will generally be provided at an angle to the axis or gas flow direction, i.e. the so-called pitch or attack angle of the vane and in a number sufficient to generate the desired centrifugal action by rotation of the gas stream. Such vanes will have leading edges which are first encountered by the oncoming gas stream and trailing edges at which the gas stream departs from contact with the vanes.
A uniflow cyclone of this type is described in German patent document - Open Application DE-OS No. 25 13 991 in which communication is afforded through perforations in the wall of the flow duct between the interior thereof and the surrounding collection chamber. The particles entrained with the gas, upon being thrown outwardly, pass through these perforations or openings in the sieve-like wall.
Experience with such apparatus has shown that the perforations in the wall give rise to a significant pressure loss in the flowing gas stream which is not turned into particle separation work. Furthermore, the cost of the unit is relatively high and hence it has not been as successful as the principles underlying such separation would appear to suggest.